overlapped Vias with the same net - How to create a rule to find the vias

There are rules to "find" the problem but not "delete" the problem.  Are you versed in scripting?  If so, you can run this SKILL routine to list, take the output to Excel, and generate a script to delete one or more of the multiple vias.  Sorry no further help than that but study this and it should help.

/*
This routine creates a report of all the vias in the design.
Open a design with vias and at the Allegro command line type:
load "myCompanyViaReport.il" <enter>
myCompanyViaReport <enter>
*/
axlCmdRegister( "myCompanyViaReport" `myCompanyViaReport)

(defun myCompanyViaReport () ; Find all of the vias in the design
allViasInDesign=list()
originalVisible=axlVisibleGet()
designName = axlCurrentDesign()
axlVisibleDesign(t)
axlShell("redisplay")
axlSetFindFilter(?enabled '(noall vias) ?onButtons '(noall vias))
allViasInDesign=axlGetSelSet(axlAddSelectAll())
axlClearSelSet()
; Open a file to work on
if(length(allViasInDesign)==0
then
axlUIConfirm("No vias in this design. Please try another design.")
else
writeOutFile = outfile("./myCompanyDesignViaReport.csv" "w")
fprintf(writeOutFile strcat("Design Via Report for " designName "\n\n"))
fprintf(writeOutFile "Via Location,Via Net Name,Padstack Name,Via Start
Layer,Via End Layer\n")
; Output data for each via to the file
foreach(via allViasInDesign
viaLocation = sprintf(nil "%L:%L" car(via->xy) cadr(via->xy))
fprintf(writeOutFile strcat(viaLocation ","))
fprintf(writeOutFile strcat(via->net->name ","))
fprintf(writeOutFile strcat(via->name ","))
fprintf(writeOutFile strcat(car(via->startEnd) ","))
fprintf(writeOutFile strcat(cadr(via->startEnd) "\n"))
);end foreach via allViasInDesign
; Close the file and wrap up
fprintf(writeOutFile "END OF FILE")
close(writeOutFile)
axlVisibleSet(originalVisible)
axlShell("redisplay")
axlUIConfirm( "Report has been generated in your working directory." )
; This next line launches Excel and displays the report
axlHttp("myCompanyDesignViaReport.csv")
);end if length(allViasInDesign)==0
);end defun myCompanyViaReport

Because these aren't coincident look at Enabling the Same net spacing rules for Via - Via. These need to be enabled using Setup - Constraint Modes - Same Net Spacing and also in Constraint Manager - Same Net Spacing Constraint Set turn on the Enable DRC by Layer. This will show a DRC flag for everything that violates the rules.